API does not returns the entire list of organization's users

Hi everybody.
When I send a GET request, the API returns the lists of users of the organization, however, the list is not complete.
A lot of users are missing. There is no pagination in the response header so and I get users sorted by first name and name in alphabetic order from B to S which is normal. Unfortunately a lot of of people are missing between each first letter.
As I don’t use any query param in the header I wonder why I encounter this problem.